The invention concerns a spring system for the upper feeder rollers in forage harvesters; in particular in a feeder device for a self-propelled forage harvester.
Spring systems are encountered in feeder systems for forage harvesters, which in the predominant number today are equipped with two lower feeder rollers carried in bearing point fixed in the feeder casing and two upper feeder rollers working together with these. The upper feeder rollers designated in the following as prepressing rollers, are carried in bearing points in the feeder casing so that their height can be altered, in order to be able to move upwards on the drawing in of harvested crop. In doing so the spring system has the task of applying a defined roll force to the prepressing rollers and to the pressing rollers, so that in conjunction with the lower feeder rollers they can on the one hand compress the crop on being drawn in and on the other hand with the aid of this roll force make possible at all the drawing-in of the crop and its transport to the cylinder chopper.
Because of the increase in performance of forage harvesters required in recent years, ever higher demands are made upon their feeder equipment, which has led on the one hand to ever wider feeder devices and higher lift heights of the prepressing roller and of the pressing roller and to a further increase in the feeding speed of the crop. These higher demands can then be fulfilled only if through the spring system the roll forces exerted by the prepressing roller and the pressing roller on the crop are at least so great that the crop cannot be pulled in from the chopper cylinder. But on the other hand they must not be so great that not just any greater accumulation of crop leads to blockages in the feeder device. The roll forces must increase significantly with growing layer thickness of the crop as a result of friction of the crop on the sidewalls of the feeder device. In the region of smaller layer thickness on the other hand, they must be kept small so that particularly in the case of the maize harvest the grains are not knocked out of the cob by too high roll forces which in the case of large chopped lengths has a particularly negative effect. Finally it is still to be pointed out that the roll forces are applied not only by the spring system, but also by the forces of reaction from the driving moment of the prepressing rollers and the pressing rollers, upon which the roller weights and frictional forces are dependent when raising and lowering them. The greater proportion comes, however, from the spring system, followed by the forces of reaction. The remaining quantities are practically negligible.
For the fulfilment of these requirements already multitudes of spring systems have become known. One of them is to be seen in the Prospectus of the German firm CLAAS for the forage harvester series xe2x80x9cJaguar 880 to 820xe2x80x9d with the note xe2x80x9c11/20 (Rihn) German 70/CVG 1106.1xe2x80x9d. Here on the shafts of the prepressing roller and of the pressing roller, on the right side viewed in the direction of travel of the forage harvester, a gearbox is placed, which is equipped at the front with a console, on which two tension springs placed inside each other engage. Their point of suspension lies plainly in front of the shaft of the prepressing roller. A single further tension spring engages from below on the gearbox about in the centre between the prepressing roller and the pressing roller. On the other hand the arrangement of the tension springs is similar, only for reasons of space they are located somewhat further up, and instead of engaging with the gearbox the tension springs engage with the oscillating crank between the prepressing roller and the pressing roller. For damping unwanted oscillations two shock absorbers are fixed on both sides of the spring system.
A disadvantage with this system is that the differences in the roll forces for a thin and a thick layer of crop are not great enough, so that either with a roll force which is set too small the crop is conveyed ever worse with increasing thickness of the layer, or in the converse case the grains are knocked out of the cobs already before the chopper cylinder. Through the described position of the attachment points of the tension springs, on the one hand it is to be criticised that with every movement of the prepressing roller the magnitude of the roll force of the pressing roller changes and the converse, because of which both roll forces are undefined. On the other hand this attachment leads to an oscillating motion of the prepressing roller and the pressing roller about the point of attachment of the tension springs, so that the aforementioned shock absorber would be necessary, which represents a cost-increasing factor. Finally with these spring systems there is yet another disadvantage, that the tension springs and the lower stops of the prepressing roller and the pressing roller lie in a zone very much endangered by dirt, so that the tension springs can no longer return to their initial lengths and on the lower stops an interfering quantity of crop collects. The consequence of this is a restricted output of the crop with a small layer thickness.
A second variant embodiment for a spring system on a feeder device for forage harvesters was made known with EP 0 797 914 B1 and as an amplification of this in the prospectus belonging to this forage harvester with the note xe2x80x9c62027/D00xe2x80x94Printed in Italyxe2x80x9412/96xe2x80x9d, in which likewise as with CLAAS on the shafts of the prepressing roller and the pressing roller a gearbox is put on. Almost centrally on the gearbox or on the oscillating crank between the prepressing roller and the pressing roller on the left side there is a pivot point, to which is attached an upwards projecting connecting rod, the upper end of which is likewise joined articulated with a swivelling lever, the other end of which ends in a bearing point attached to the casing of the feeder device. In a forwards projecting connecting bracket on the connecting rod a tension spring is suspended by its upper end and is fixed with its lower end to the front on the easing of the feeder device. As this spring system exhibits the same disadvantages as afore-described one, to avoid repetition reference will be made at this point only to this one.
A third possibility for the design of a spring system for the upper feeder rollers is expounded in EP 1 151 658 A1. The only difference from the two previously described ones consists in that instead of two upper feeder rollers three are employed here. As the coupling of the two tension springs on each side is in principle executed the same as for the two previously described spring systems; the same disadvantages apply here too.
In the prospectus of the German firm MENGELE with the note xe2x80x9cWA FITZEK/1/94xe2x80x9410xe2x80x9d a self-propelled forage harvester of the type xe2x80x9cMAMMUTxe2x80x9d with a feeder device and spring system for the upper feeder rollers is depicted. Here the roll force acting on the prepressing roller is produced by two tension springs, and that for the pressing roller is produced by a tension spring one on each side. Although here the directions of pull of the tension springs in the lowest position of the prepressing roller and of the pressing roller appear at first glance to be somewhat more favourable than in the three previously described spring systems, it is nevertheless to be criticised, that with the differently large excursions the position of the tension is so far removed from the shafts of the rollers, that every movement of the prepressing roller changes the magnitude of the roll force of the pressing roller and vice versa. In the same way the disadvantage remains of the too small difference in the roll forces for a thin and a thick layer of crop. Also the soiling of the tension springs and of the lower stops is unavoidable here, so that also the disadvantages associated with this exist.
Finally, reference would be made to the feeder device with upper feeder rollers and a spring system in accordance with DE-OS 26 09 272, in which the prepressing roller and the pressing roller are carried in bearing points in an approximately vertical orientation in the side walls so that they can be moved independently of each other. Each of the upper feeder rollers obtains its drive separately via a cardan shaft. The roll force is produced here by compression springs, which are abut with their upper ends on the casing of the feeder casing and which press with their lower ends on the bearing of the prepressing roller or the pressing roller. For adjusting the roll force the upper ends are held in threaded couplings, which are vertically adjustable by means of threaded spindles. Although through the separate drives the reaction forces resulting from them are practically excluded, this solution too has still some disadvantages attached to it. These are that also here there are too small differences in the roll forces with differing thicknesses of the layer of harvested crop and the position of the lower stops for the prepressing roller and the pressing roller in the area of greatest soiling with dirt. Furthermore, with the increasing of the roll force the upper stop is displaced downwards, so that the maximum height of lift thereby experiences a restriction. Besides, through the possibility of movements of both rollers completely independently of each other blockages can occur in the event that the prepressing roller is raised up to the upper stop and the pressing roller remains below. Therefore the task of the invention is to create a spring system for the upper feeder roller of a forage harvester, in which the roll forces increase distinctly with growing thickness of the layer of the harvested crop, where the springs envisaged for the prepressing roller load only this roller over the whole lifting path and not the pressing roller and vice versa, the springs of which are situated in a space less burdened with dirt and in which the upper and the lower stops of the rollers are so formed and arranged, that the prepressing roller and the pressing roller actually come again always into this same position regardless of deposits of dirt.
For the present feeder device with two upper feeder rollers the front prepressing roller and the pressing roller arranged behind it are attached opposite two lower feeder rollers carried in bearing points at a fixed location in the casing of the feeder device so that their distance can be varied, as a result of which they can swing between their lowest and uppermost position according to the supply of crop. So that on the one hand they can pre-compress the crop well in combination with the lower feeder roller and on the other hand be able to transport it to the chopping device, they have the necessary roll force applied to them by means of the compression springs with their upper ends abutting with the casing of the feeder device and with their lower ends supported on the bearing point points of the upper feeder rollers. The compression springs are held in position with guide rods, onto which they are placed concentrically and their upper ends are attached to the casing of the feeder device so that they can move freely.
For the prepressing roller two compression springs are employed, one of which exerts a small roll force on it already in the lowest position of the prepressing roller. The second compression spring remains without effect over the first stretch of its lifting path from the lowest position and engages only later with its upper end on the casing of the feeder device, as a result of which then its roll forces add up to a very great roll force. Through this high roll force it is possible without any problems, to exclude the forces of reaction arising from the drive moments of the upper roller on the prepressing roller, which with an appropriate management of the drive relieve the prepressing roller, without negative influences on the precompresssion and transport at the this point. The roll force for the prepressing roller is produced by a compression spring, which already in its lowest position is under a slight prestress and which over the entire lifting path of the pressing roller exerts a distinctly lower roll force on it than do the two compression springs on the prepressing roller. Consequently, with the same drive management as described above the forces of reaction arising from the driving moments for the upper roller bear down on the pressing roller from above and press it onto the crop, so that it is even possible to dispense with these compression springs altogether.
As a precaution, all the spring systems for the prepressing roller lie within the wishes of protection of the invention, which exhibit a progressively rising spring characteristic and differ in detail from the previously described solution. Also specially formed single compression springs or systems with more than two springs fall under this protection.
In this spring system, the area of small layer thicknesses exerts only small roll forces on the crop and with growing layer thickness the roll forces increase distinctly. The direction of the roll forces on the bearing points as close and possible to the central axes of the shafts of the prepressing roller and of the pressing roller lead to their defined loading without mutual influencing of each other. Through the position of the compression springs and the upper and lower stops for limiting the freedom of movement of the upper feeder rollers in their uppermost and lowest position in a largely dirt free space their unchanged position over a long time is ensured.